1. Field of the Invention
The present invention relates to an X-ray detector preferably usable for medical computer tomography (X-ray CT) and the like requiring particularly high time resolution and spatial resolution.
2. Description of the Related Art
Recently, X-ray computer tomography (X-ray CT) is employed for the diagnosis of an internal organ which beats extremely fast such as a heart. In order to photograph finely such an internal organ as beating extremely fast, a detector satisfying high time resolution and high spatial resolution is required.
At present, an indirect conversion type X-ray detector, which converts an X-ray into a visible light once by a scintillator and then, converts the visible light into the corresponding electric signal, is mainly employed for the X-ray computer tomography. In the indirect conversion type X-ray detector, however, the enhancement of the time resolution is pushed to the limit due to the afterglow of the scintillator. In this point of view, such a direct conversion type X-ray detector as directly converting an X-ray with semiconductor is proposed instead of the indirect conversion type X-ray detector (Reference 1).
The direct conversion type X-ray detector in Reference 1 is configured such that a platy electrode is formed on the X-ray incident surface of a CdTe semiconductor substrate and a plurality of pixel electrodes are arranged on the rear surface of the semiconductor substrate opposite to the X-ray incident surface thereof, and a signal reading circuit (CMOS) with electrode pads electrically connected with the pixel electrodes respectively via soldering portions is provided.
In the direct conversion type X-ray detector, the charged particles (electrons and holes) caused by the incidence of an X-ray onto the semiconductor substrate are detected at the pixel electrodes under the condition that a constant biasing voltage is applied between the platy electrode and the pixel electrodes, and read out at the signal reading circuit. Since the amount of the charged particles detected at the pixel electrodes is proportional to the intensity of the incident X-ray, the incident position into the X-ray detector can be known by measuring the amount of the charged particles, that is, the amplitude of the electric signal corresponding to the charged particles per pixel electrode.
With the direct conversion type X-ray detector, however, the X-ray can not be often detected in high spatial resolution in dependence on the intensity of the X-ray and the like.
[Reference 1] Radiation, Vol. 30, No. 1, p1 (2004)